Tellurium (Te) Precursors for Making Phase Change Memory Materials

ABSTRACT

Tellurium (Te)-containing precursors, Te containing chalcogenide phase change materials are disclosed in the specification. A method of making Te containing chalcogenide phase change materials using ALD, CVD or cyclic CVD process is also disclosed in the specification in which at least one of the disclosed tellurium (Te)-containing precursors is introduced to the process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/100,824, filed on Apr. 10, 2008, which claims the benefit ofpriority under 35 U.S.C. § 119(e) to earlier filed U.S. patentapplication Ser. No. 60/913,798, filed on Apr. 24, 2007. The disclosuresof those applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Phase-change materials exist in a crystalline state or an amorphousstate according to temperature. A phase-change material has a lowerresistance and a more ordered atomic arrangement in a crystalline statethan in an amorphous state. A phase-change material can be reversiblytransformed from the crystalline state to the amorphous state based onan operating temperature. Such characteristics, that is, reversiblephase change and different resistances of different states, are appliedto newly proposed electronic devices, a new type of nonvolatile memorydevices, phase-change random access memory (PRAM) devices. A resistanceof a PRAM may vary based on a state (e.g., crystalline, amorphous, etc.)of a phase-change material included therein.

Various types of phase-change material can be used for memory devices,the most commonly used phase change materials are ternary composition ofchalcogenides of group 14 and group 15 elements, such asgermanium-antimony-tellurium compounds, commonly abbreviated as GST. Thesolid phases of GST can rapidly change from crystalline to amorphous orvise versa upon heating and cooling cycles. The amorphous GST hasrelatively higher electric resistance and the crystalline GST hasrelatively lower electric resistance.

Currently, Physical Vapor Deposition (PVD) processes, or spattering, areused in the manufacture of re-writable optical disks to coat a thinlayer of phase change material on the plastic substrates. However, thePVD processes are not suitable for electronic devices due to film growthcontrol and film properties. To make PRAM, Chemical Vapor Deposition(CVD), or Atomic Layer Deposition (ALD) techniques are used to deposit athin film of GST on the substrate of silicon. The development ofphase-change memory devices raises the need for ALD/CVD processes withproper precursors for low temperature deposition.

BRIEF SUMMARY OF THE INVENTION

The present invention satisfies the need by providing thetellurium-containing compounds as Te precursors for deposition ofternary germanium-antimony-tellurium films by low temperature ALD, CVDor cyclic CVD processes.

A Te containing composition is disclosed in the specification. The Tecontaining composition comprises deuterated an organotellurol having ageneral structure of:

-   -   R—Te—D        wherein R is selected from the group consisting of an alkyl        group or an alkenyl group having 1 to 10 carbons in linear,        branched, or cyclic form; an aromatic group having C₆-C₁₂; a        dialkylamino group; an organosilyl group; an organogermyl; and D        is deuterium.

A Te containing chalcogenide phase change material is disclosed in thespecification. The Te containing chalcogenide phase change material isprepared by depositing a Te precursor selected from the group consistingof

-   -   (a) an organotellurol having a general structure of:        -   R-Te-R′    -   wherein R is selected from the group consisting of an alkyl        group or an alkenyl group having 1 to 10 carbons in linear,        branched, or cyclic form; an aromatic group having C₆-C₁₂; a        dialkylamino group; an organosilyl group; and an organogermyl;        and R′ is selected from the group consisting of hydrogen and        deuterium;    -   (b) a composition having a general structure of: R″₂Te wherein        R″ is selected from the group consisting of hydrogen and        deuterium; and    -   (c) tellurium hexafluoride.

A process of depositing Te containing chalcogenide phase change materialon a substrate is also disclosed in the specification. The processcomprises steps of:

depositing a Te precursor comprising a Te-containing compositionselected from the group of:

-   -   (a) an organotellurol having general structure of:        -   R—Te—R′    -   wherein R is selected from the group consisting of an alkyl        group or an alkenyl group having 1 to 10 carbons in linear,        branched, or cyclic form; an aromatic group having C₆-C₁₂; a        dialkylamino group; an organosilyl group; and an organogermyl;        and R′ is selected from the group consisting of hydrogen and        deuterium;    -   (b) a general structure of:        -   R″₂Te    -   wherein R″ is selected from the group consisting of hydrogen and        deuterium; and    -   (c) tellurium hexafluoride reacting with ammonia; depositing a        Ge precursor comprising aminogermanes having a general structure        of:        -   (R¹R²N)₄Ge    -   wherein R¹ and R² are alkyl groups having 1 to 10 carbons in        linear,    -   branched, or cyclic form; and

depositing a Sb precursor comprising aminostibanes having a generalstructure of:

-   -   (R¹ R²N)₃Sb

wherein R¹ and R² are alkyl groups having 1 to 10 carbons in linear,branched, or cyclic form.

The three deposition steps in the process can be carried outsequentially in any order or concurrently. Or, any two of threedeposition steps can be carried out concurrently. The process is carriedout at 100-400° C. by ALD, CVD, or cyclic CVD processes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to selected tellurium compounds as Teprecursors, and using the selected tellurium compounds along withaminogemanium and aminoantimony compounds, in a low temperature processto produce ternary germanium-antimony-tellurium films via ALD, CVD orcyclic CVD processes.

In one embodiment of the present invention, the Te precursor for lowtemperature deposition process comprises hydrogen telluride (H₂Te).Aminometal compounds are reactive toward hydrolysis. Hydrogenchalcogenides are all more acidic than water. The reactions ofaminogermanes and aminoantimony with hydrogen telluride form metaltellurides at low temperature (<250° C.).The deposition oftetrakis(dimethylamino)germane, (Me₂N)₄Ge, andtris(dimethylamino)antimony, (Me₂N)₃Sb, followed by the treatment withhydrogen telluride is a suitable approach for ALD or CVD processes ofmaking GST films for phase change memory applications. Hydrogentelluride is a gaseous compound with a boiling point of −4° C. It isunstable above 0° C., and it decomposes into elemental tellurium andhydrogen. To overcome this problem, hydrogen telluride can be producedby in situ generation, and immediately introduced into the reactionchamber.

In another embodiment of the present invention, the Te precursorcomprises deuterium telluride (D₂Te). Deuterium is the heavier isotopeof hydrogen (where the nucleus has an added neutron). Deuteriumtelluride has improved thermal stability, compared with thecorresponding regular hydrogen telluride.

As more thermally stable tellurium compounds, organotellurols anddeuterated organotellurols are disclosed as more suitable telluriumprecursors for ternary germanium-antimony-tellurium film depositions.

In another embodiment of the present invention, the Te precursor for lowtemperature deposition process comprises organotellurols.Organotellurols have acidic Te-H bonds, which are highly reactive to theGe—N and Sb—N bonds in the corresponding aminometal compounds. Te—Ge andTe—Sb bonds form at relatively low temperature, with the volatile aminesas leaving compounds. The reaction is illustrated in the followingscheme:

The Te precursor comprising organotellurols has a general formula of

-   -   R—Te—R′        where R is an alkyl group or alkenyl group having 1 to 10        carbons in linear, branched, or cyclic form; or an aromatic        group having C₆-C₁₂, such as phenyl; or a dialkylamino group; or        an organosilyl group; or an organogermyl group; R′ is hydrogen        or deuterium.

Alkyl tellurols are the preferred tellurium precursors. They arevolatile liquids and can be delivered by vapor draw or direct liquidinjection methods. T-Butyltellurol has a weak Te—C bond with a bondenergy of 26 kcal/mole. The t-butyl group can be cleaved at relativelylow temperature. This helps to reduce the carbon content in theresulting GST films.

Deuterated organotellurols have improved thermal stability, comparedwith the corresponding regular organotellurols, resulting in longershelf life and wider process windows. Due to the primary kinetic isotopeeffect, Te—D bond is more stable than Te—H bond. Therefore, deuteratedorganotellurols have less tendency to decompose during storage anddelivery, while maintaining the similar chemical reactivity to formtellurides with germanium and antimony.

Examples of Te precursors comprising deuterated organotellurols areN-Butyltellurol-D and T-Butyltellurol-D, where “D” is deuterium.

In another embodiment of the present invention, the Te precursorcomprises tetrakis(dialkylamino)tellurium, wherein, the alkyl group isindependently selected from the group consisting of methyl, ethyl,propyl, isopropyl, butyl, and t-butyl.

The Te precursor comprising tetrakis(dimethylamino)tellurium can bemixed with tetrakis(dimethylamino)germanium (Me₂N)₄Ge andtris(dimethylamino)stilbane to form uniform solutions in desired molarratios. Such a solution is introduced to the deposition chamber bydirect liquid injection methods. The chemicals are deposited on thesurface of a heated substrate. The following reduction reaction byhydrogen or hydrogen plasma removes the amino groups and forms a GSTlayer with the proper elemental ratio. These steps form a cycle for ALDor cyclic CVD process.

In yet another embodiment of the present invention, the Te precursorcomprises tellurium hexafluoride. Tellurium hexafluoride TeF₆ is acolorless gas with a boiling point of −38° C. Unlike the sulfur analog,tellurium hexafluoride is not chemically inert. This can be attributedto the greater availability of the d orbital and perhaps theavailability of the f orbital, which neither sulfur nor selenium hasaccess to.

In another embodiment of the present invention, Te containingchalcogenide phase change material is prepared by depositing a Teprecursor selected from any of previous disclosed embodiments, via anyknown deposition method, such as by ALD, CVD, or cyclic CVD processes.

In yet another embodiment of the present invention, the process ofmaking a Te-containing chalcogenide phase change material, may employdepositing a Te precursor from any of previous disclosed embodimentswith a Ge precursor and a Sb precursor via any known deposition method,such as by ALD, CVD, or cyclic CVD processes.

Examples of a Ge precursor and a Sb precursor are aminogermanes andaminostibanes having the general structures of:

-   -   (R¹R²N)₄Ge and (R¹R²N)₃Sb        Where R¹ and R² are independently alkyl groups having 1 to 10        carbons in chain, branched, or cyclic form.

For example, as a tellurium precursor, tellurium hexafluoride can reactwith ammonia in a deposition chamber to form aminotellurium, which maysubsequently react with aminogermanes and aminostibanes, followed byhydrogen reduction to generate GST films on a substrate.

-   -   TeF₆+NH₃---->[Te(NH₂)_(n)]+NH₄F

In the process for making the GST thin films, three precursors can bedeposited sequentially. Any one of the three precursors, such as the Geprecursor is deposited on the surface of a heated substrate that has asuitable temperature for the chemical reaction. After a purging/cleaningstep, such as by flowing inert gas, the second precursor, such as the Sbprecursor is deposited on the surface of the substrate having Ge thinlayer. After another purging/cleaning step, the last precursor, such asthe Te precursor is deposited on the substrate having Ge and Sb thinlayer. Any one of the three precursors can be the first or the second orthe third precursors for the process. For the purpose of the presentinvention, depositing on a substrate includes not only depositiondirectly on the substrate itself, but also deposition on one at theother of the three reactants already deposited on the substrate.

Alternatively, the deposition process can deposit any two of the threeprecursors concurrently, or all three precursors concurrently.

In addition, the deposition process can be repeated to make multi-layerfilms.

The film deposition can be carried out at 100-400° C.

Working Examples

In preparing the Te precursor for lower temperature deposition, any ofthe various known methods, may be employed. Among the known methods, amethod of preparing the Te precursor according to embodiments of theexamples of the present invention is described as follows.

Example I Synthesis of N-Butyltellurol-D

6.4 g (0.05 mol) 200 mesh tellurium powder, 100 ml diethyl ether, and 20ml 2.5 M n-butyllithium in hexane were added to a 250 ml flask. At 0°C., the mixture was stirred for 8 hours. All black powder of telluriumdisappeared and a muddy color precipitate was formed. To this mixture,5.4 g (0.05 mol) trimethylchlorosilane was added. The mixture wasallowed to warm up to room temperature. After stirring for 2 hours, 2.0g (0.06 mol) deuterated methanol (MeOD) was added slowly. After stir for1 hour, the mixture was filtered under inert atmosphere. The solvent andby product methoxytrimethylsilane were removed by distillation. A vacuumdistillation gave N-Butyltellurol-D. The boiling point is 85° C./100mmHg.

Example II Synthesis of T-Butyltellurol-D

12.8 g (0.10 mol) 200 mesh tellurium powder, 250 ml diethyl ether, and50 ml 2.0 M t-butylmagnesium chloride solution in diethyl ether wereadded to a 500 ml flask. At room temperature, the mixture was stirredfor 24 hours. All black powder of tellurium disappeared and a light graycolor precipitate was formed. The mixture was cooled to −50° C. with adry ice bath. To this mixture, 10.0 g (0.21 mol) deuterated ethanol(EtOD) was added slowly. The mixture was allowed to warm up to roomtemperature. After stirring for 2 hours, the mixture was filtered underinert atmosphere. The solvent ether was removed by distillation. Avacuum distillation gave T-Butyltellurol-D. The boiling point is 65°C./100 mmHg.

The embodiments of this invention listed above, including the workingexample, are exemplary of numerous embodiments that may be made of thisinvention. It is contemplated that numerous other configurations of theprocess may be used, and the materials used in the process may beelected from numerous materials other than those specifically disclosed.

1. A process of depositing Te containing chalcogenide phase changematerial on a substrate, comprising steps of: depositing a Te precursorcomprising an organotellurol having a general structure of: R—Te—R′wherein R is selected from the group consisting of an alkyl group or analkenyl group having 1 to 10 carbons in linear, branched, or cyclicform; an aromatic group having C₆-C₁₂; a dialkylamino group; anorganosilyl group; and an organogermyl; and R′ is selected from thegroup consisting of hydrogen and deuterium; depositing a Ge precursorcomprising aminogermanes having a general structure of: (R¹R²N)₄Gewherein R¹ and R² are alkyl groups having 1 to 10 carbons in linear,branched, or cyclic form; and depositing a Sb precursor comprisingaminostibanes having a general structure of: (R¹R²N)₃Sb wherein R¹ andR² are alkyl groups having 1 to 10 carbons in linear, branched, orcyclic form; and
 2. The process of claim 1, wherein the organotellurolis selected from the group consisting of N-Butyltellurol-D andT-Butyltellurol-D.
 3. The process of claim 1, wherein the processfurther comprising a step of introducing hydrogen or hydrogen plasmaafter each step of depositing; or after all three steps of depositing.4. The process of claim 1, wherein at least two depositing steps arecarried out concurrently.
 5. The process of claim 1, wherein thedepositing is carried out by a process selected from the groupconsisting of ALD, CVD, and cyclic CVD process.
 6. The process of claim2, wherein the depositing is carried out by a process selected from thegroup consisting of ALD, CVD, and cyclic CVD process.
 7. A Te containingchalcogenide phase change material synthesized by the process of claim5.
 8. A Te containing chalcogenide phase change material synthesized bythe process of claim
 6. 9. A process of depositing Te containingchalcogenide phase change material on a substrate, comprising steps of:depositing a Te precursor comprising a Te-containing composition havinga general structure of: R″₂Te wherein R″ is selected from the groupconsisting of hydrogen and deuterium; depositing a Ge precursorcomprising aminogermanes having a general structure of: (R¹R²N)₄Gewherein R¹ and R² are alkyl groups having 1 to 10 carbons in linear,branched, or cyclic form; and depositing a Sb precursor comprisingaminostibanes having a general structure of: (R¹R²N)₃Sb wherein R¹ andR² are alkyl groups having 1 to 10 carbons in linear, branched, orcyclic form.
 10. The process of claim 9, wherein the process furthercomprising a step of introducing hydrogen or hydrogen plasma after eachstep of depositing.
 11. The process of claim 9, wherein the processfurther comprising a step of introducing hydrogen or hydrogen plasmaafter the three steps of depositing.
 12. The process of claim 9, whereinat least two depositing steps are carried out concurrently.
 13. Theprocess of claim 9, wherein the depositing is carried out by a processselected from the group consisting of ALD, CVD, and cyclic CVD process.14. A Te containing chalcogenide phase change material synthesized bythe process of claim
 13. 15. A process of depositing Te containingchalcogenide phase change material on a substrate, comprising steps of:depositing a Te precursor comprising aminotellurium by reactingtellurium hexafluoride with ammonia; depositing a Ge precursorcomprising aminogermanes having a general structure of: (R¹R²N)₄Gewherein R¹ and R² are alkyl groups having 1 to 10 carbons in linear,branched, or cyclic form; and depositing a Sb precursor comprisingaminostibanes having a general structure of: (R¹R²N)₃Sb wherein R¹ andR² are alkyl groups having 1 to 10 carbons in linear, branched, orcyclic form.
 16. The process of claim 15, wherein the process furthercomprising a step of introducing hydrogen or hydrogen plasma after eachstep of depositing.
 17. The process of claim 15, wherein the processfurther comprising a step of introducing hydrogen or hydrogen plasmaafter all three steps of depositing.
 18. The process of claim 15,wherein at least two steps of depositing are carried out sequentially orconcurrently.
 19. The process of claim 15, wherein the depositing iscarried out by a process selected from the group consisting of ALD, CVD,and cyclic CVD process.
 20. A Te containing chalcogenide phase changematerial synthesized by the process claim 19.